Hi Baldovin, thank you for reaching out.
Although we do have a free "Find Company Headcount Growth" enrichment, which I recommend you look at, this enrichment only looks at company headcount growth as a whole. As such, I do believe that using Claygent would be the best option to find the Headcount growth by department through information on LinkedIn. To do so, in the Claygent prompt, write the information you would want to retrieve from LinkedIn and also give it some sources (company domain or LinkedIn website) where this information can be found.
I will also make sure to report back to our engineering team and suggest they add a new functionality that returns headcount growth in a specific department over time.
Please let me know if there is anything else I can help you with